Apparatus for controlling the bulk density of coal



April 14, 1970 w. A. RAUDENBUSH 3,506,200

APPARATUS FOR CONTROLLING THE BULK DENSITY OF COAL Filed May 5, 1968 CONTROL 36 R607) A 0/70 (ELL .38 TR/M/SDI/Cfl INVENTOR United States Patent 3,506,200 APPARATUS FOR CONTROLLING THE BULK DENSITY 0F COAL William A. Raudenbush, Hellertown, Pa., assignor to Bethlehem Steel Corporation, a corporation of Delaware Filed May 3, 1968, Ser. No. 726,289 Int. Cl. G07b 11/08 US. Cl. 241-41 Claims ABSTRACT OF THE DISCLOSURE Signals indicative of the height and weight of coal on a predetermined surface area of a conveyor belt are combined to produce an output signal indicative of the bulk density of the coal. The output signal is utilized to control the addition of a bulk density-changing substance to the coal as it enters a hammer mill.

BACKGROUND OF THE INVENTION This invention relates to apparatus for controlling the bulk density of coal, and more particularly to apparatus for adding a bulk density-changing substance to coking coal if the bulk density thereof differs from a desired value.

One of the most important factors affecting the quality of coke is the bulk density of the coal which is charged into the oven. Changes in bulk density cause varying heating rates and pressures, which result in coke of varying quality.

The principal cause of changes in bulk density is changes in the moisture content on the surface of the coal. As the surface moisture increases, the coal increases in volume and its bulk density decreases. Conversely, as the surface moisture decreases, the coal decreases in volume and its bulk density increases.

It is generally believed that some moisture is desirable in a coke oven charge. However, the moisture content of the coal is highly dependent on the weather, and may be either less than or greater than the optimum amount.

It has heretofore been known that the bulk density of wet coal can be increased by the addition of oil thereto, and apparatus has been devised for adding oil or Water to coking coals to increase or decrease respectively the bulk density thereof. However, in general, such apparatus required coal being conveyed from the hammer mill to the coke ovens to be of a constant height on the conveyor belt in order for accurate bulk density determinations to be made. It has been found that, due to varying production rates, for example, from 600 tons/hr. to 750 tons/hr. there is no practical, simple way to maintain a constant coal height on said conveyor belt.

It is an object of this invention to provide an apparatus for maintaining the bulk density of coal constant. It is a further object to provide such an apparatus wherein the height of the coal on the conveyor belt conveying the coal to the coke ovens need not be constant.

SUMMARY OF THE INVENTION I have discovered that the foregoing objects can be attained by providing apparatus comprising a hammer mill for pulverizing coal, a conveyor belt for receiving the coal from the hammer mill and conveying the coal to coke ovens, a device disposed above said belt for producing a first signal indicative of the height of said coal on said belt, a device disposed below said belt for producing a second signal indicative of the weight of said coal on a predetermined surface area of said belt, a device for combining said first and second signals to produce an output signal indicative of the bulk density of the coal disposed on said surface area, means for adding a bulk density changing substance to said coal as it enters the hammer mill, and means for controlling the addition of said substance in response to said output signal.

BRIEF DESCRIPTION OF THE DRAWING The sole drawing is a diagrammatic view of the subject apparatus.

DESCRIPTION OF THE PREFERRED EMBODIMENT As shown in the drawing, coal 10, which has been blended and mixed in a mixing mill (not shown), is transported by a conveyor belt 12 to a hammer mill 14. The hammer mill 14 comprises a hopper 16, rotating hammers l8, grate bars 20, and a discharge chute 22. Below the chute 22 is a conveyor belt 24 which transports the coal pulverized in the hammer mill 14 to the coke ovens.

Disposed above the conveyor belt 24 is means for producing a first signal indicative of the height of the coal thereon. This means comprises a standard pneumatic transmitter 26 having the pilot rod 28 thereof connected to an arm 30 pivotally mounted with respect to pivot point 32. The end of the arm 30 is provided with a plate 34 which maintains contact with the top of the coal 10. As the height of the coal on the belt varies, the pilot rises or falls, thereby controlling the output pressure of the pneumatic transmitter 26.

Disposed below the conveyor belt 24 is means for producing a second signal indicative of the weight of said coal on a predetermined surface area of said conveyor belt. Said means comprises a load cell 36 which produces an electrical signal indicative of said weight. This electrical signal is supplied to a transducer 38 which converts said signal into a pneumatic signal.

The outputs from the pneumatic transmitter 26 and the transducer 38 are connected to the inputs of a pneumatic multifunction relay 40. The relay 40 combines said outputs to produce an output signal indicative of the bulk density of the coal disposed on the surface area above the load cell 36.

Broadly, the multifunction relay 40 comprises two contiguous chambers connected to a pilot valve which controls the output signal from said relay. The output from the transmitter 26 is connected to one chamber, while the output from the transducer 38 is connected to the other chamber. As long as the ratio of these outputs remains constant, e.g. 1:1, the output from the relay 40 remains constant, while changes in said ratio result in an increase or a decrease in the output from the relay 40.

A water pipe 42 and an oil pipe 44 are mounted with their outlets 46 and 48, respectively, disposed at the inlet of the hammer mill 14. The other ends of the pipes are respectively connected to a water storage tank 50 and an oil storage tank 52, pneumatic control valves 54 and 56 being provided for regulating the How of liquid from said tanks.

The output of the relay 40 is connected to a pneumatic controller 58 which provides the pressure to control the valves 54 and 56. The controller 58 operates as follows. If the bulk density of the coal is correct, the output signal from the relay 40 is balanced by an input bias signal in the controller 58, and the controller produces an output signal which causes both valves 54 and 56 to remain stationary. However, if the bulk density is too low, for example, the signal from the relay 40 is not balanced by the bias signal, and the output signal from the controller 58 begins to decrease, causing the valve 56 to start to open (assuming that both valves are initially closed). The output from the controller continues to decrease, causing the valve 56 to continue to open, until the signal from the relay 40 is balanced by the bias signal. The output from the controller then remains at whatever value it had reached when balance was attained, causing the valve 56 to remain in its position at balance as long as said balance is maintained. Should the bulk density then increase beyond the desired value, the output signal from the relay 40 is again not balanced by the bias signal in the controller 58; however, in this case, the unbalance is opposite to the previous unbalance, and the output signal from the controller 58 begins to increase, causing the oil valve 56 to begin to close. The output from the controller continues to increase, causing the valve 56 to continue to close, until the input signal from the relay 40 is again balanced by the bias signal. It is possible that the bulk density of the coal may exceed the desired value by an amount so great that the oil valve 56 will completely close and the water valve 54 will then begin to open.

The transmitter 26 and the load cell 36 are so disposed with respect to the water and oil outlets 46 and 48, respectively, that about one minute elapses from the time the coal passes said outlets to the time the same coal reaches the transmitter and the load cell. Thus, the elfect of adding oil, for example, to the coal will not be immediately sensed by the aforementioned control devices. For this reason, the controller 58 is designed so that the output thereof does not change rapidly in response to a signal from the relay 40. The output from the controller "58 changes sufficiently slowly so that the water valve 54 or oil valve 56 will open or close relatively slowly.

The following is a specific example of my invention.

Coal which has been pulverized until 78% thereof will pass through a V8 inch screen has a bulk density of 45 lbs/ft. when the moisture thereof is optimum, viz about 4%. It has been found that coal of this bulk density has a height of 7.5 inches on belt 24 when the weight on the load cell 36 corresponds to a rate of 750 tons/hr.

In view of the foregoing, the transmitter 26 was calibrated to produce an output signal of 12 p.s.i.g. when the height of the coal on the belt 24 was 7.5 inches and the transducer 38 was calibrated to produce an output signal of 12 p.s.i.g. when the weight on the load cell 36 corresponded to a rate of 750 tons/ hr. The multifunction relay 40 was adjusted to have an output of 9 p.s.i.g. when the pressure at the two inputs was in a ratio of 1:1. The controller 58 was provided with an input bias signal of 9 p.s.i.g., and an initial output (the set point) of 9 p.s.i.g. The output from the the controller could subsequently vary from to 15 p.s.i.g. The valves 54 and 56 were adapted to be closed when the input thereto was 9 p.s.i.g., while the oil valve 56 would open at input pressures less than 9 p.s.i.g. and the water valve would open at input pressures greater than 9 p.s.i.g.

Initially, both valves 54 and 56 were closed and coal was supplied to the conveyor belt 24 at a rate of 600 tons/hr. The coal had a bulk density of about 43.5 lbs./ft. The height of the coal on the conveyor belt was 6.9 inches.

In response to said coal, the load cell 36 produced a signal of 3.96 mv., which was converted by the transducer 38 into a pneumatic signal of 10.2 p.s.i.g. The pneumatic transmitter 26 produced a signal of 11.28 p.s.i.g., said signal and the signal from the transducer being supplied to the relay 40 The output from the relay 40 was initially 7.92 p.s.i.g., said signal being supplied to the controller 58. The output from the controller 58 immediately began to gradually decrease from its initial value of 9 p.s.i.g., causing the oil valve 56 to begin opening. The output from the controller 58 continued to gradually decrease and in about 3 minutes was about 3 p.s.i.g., at which time the oil valve was almost completely open. During the time the oil valve was opening, the signal supplied to the controller 58 from the relay 40 gradually increased to 9 p.s.i.g. At this point, oil was passing out of the valve 56 at a rate of 165 gal./hr., and the bulk density of the coal was 45.0 lbs/ft The bulk density of the coal subsequently increased to 45.33 lbs./ft. The height of the coal on the conveyor belt 24 was 5.8 inches, and the output from the trans. mitter 26 decreased to 9.96 p.s.i.g. The output from the transducer 38 remained at 10.2 p.s.i.g., as the coal was still being supplied to the conveyor belt 24 at a rate of 600 tons/hr. In response to the signals from the transmitter 26 and the transducer 38, the relay 49 produced an output of 10.44 p.s.i.g. The output from the controller 58 immediately began to gradually increase to 4 p.s.i.g., causing the oil valve 56 to close slightly. At this point, oil was passing out of the valve 56 at a rate of gal./hr., and the bulk density of the coal had returned to 45.0 lbs./ft.

All of the pneumatic components hereinbcfore mentioned are standard and well known in the art.

I claim:

1. Apparatus for controlling the bulk density of coa comprising:

(a) means for continuously conveying coal,

(b) means for producing a first signal indicative of the height of said coal on means (a),

(c) means for producing a second signal indicative of the weight of said coal on a predetermined surface area of means (a),

(d) means, connected to means (b) and (c), for combining said first and second signals to produce an output signal indicative of the bulk density of the coal disposed on said surface area,

(e) means for adding a bulk density-changing substance to the coal to be conveyed, and

(f) means for controlling means (e) in response to said output signal.

2. Apparatus as recited in claim 1, in which:

(i) means (d) produces an output signal dependent upon the ratio of said first and second signals,

(ii) means (e) comprises storage means for said bulk density-changing substance and valve means for controlling the rate of addition of said substance to the coal to be conveyed, and

(iii) means (f) is adapted to open or close said valve means until said output signal equals a predetermined value.

3. Apparatus as recited in claim 1, further comprising (g) means for pulverizing said coal, in which:

(i) means (a) comprises a conveyor belt adapted to receive coal from means (g), and

(ii) means (e) is adapted to add said bulk densitychanging substance to said coal while said coal is in means (g).

4. Apparatus as recited in claim 3, in which means (b) comprises a device, disposed above said conveyor belt, having a movable element in contact with the surface of said coal, the magnitude of said first signal being a function of the position of said movable element.

5. Apparatus as recited in claim 3, in which means (e) comprises:

(i) water storage means communicating with means (ii) oil storage means communicating with means (g),

and

(iii) valve means for controlling the flow of liquid from said water storage means and said oil storage means.

References Cited UNITED STATES PATENTS 2,510,158 6/1950 Van Ackeren 24141 2,864,537 12/1958 Throop et a1. 24134 GERALD A. DOST, Primary Examiner US. Cl. X.R. 24l33, 62 

